Bio-inspired surfaces for turbulence reduction

While the topic of bio-inspired flow control has been an area of active study since early in the last century, there has been renewed interest in recent years in both passive (shark skin) and active (dolphin skin) methods of flow control to reduce hydrodynamic drag and boundary layer turbulence. This renewed interest is mainly due to advances in technology, in particular additive manufacturing, soft robotics, and microelectronics. In this work, we investigate the impact of shark skin denticle surfaces, as well as actively modulated boundaries with and without added roughness elements, on near-boundary velocity to improve our understanding of the underlying mechanism and work towards implementation in underwater platforms. We developed a set of shark-skin inspired denticle inserts and soft membranes using advanced additive manufacturing techniques and characterized the impact on the velocity field in a flow channel under varying flow conditions. Accompanying high-order numerical simulations show a change in vorticity over the denticle-covered surface, in a pattern consistent with laboratory experiments. The respective changes to the velocity profile provide guidance for implementation of boundary layer control methods (active and passive) on in-water vehicles.